‘ 
ELEMENTARY BACTERIOLOGY LABORATORY EXERCISES 49 
To the above, just before using, add: 
Sodium sulphite (anhydrous) 0.25% 
Basic fuchsin (10% alcoholic solution) ........-----:------------ 0.5% 
In this medium, when properly prepared, the sodium sulphite solution decol- 
orizes the intense red of the fuchsin to a light pink. Organisms of the coli-aero- 
genes type change the medium to a bright red color and their colonies usually 
show a metallic luster. The coli types, as a rule, produce a more pronounced me- 
tallic luster than do the aerogenes types. 
EXERCISE 74 
EOSINE-METHYLENE BLUE AGAR 
In the same manner as with Endo medium, plate the same cultures on eosine- 
methylene blue agar and incubate at 37° C. 
The composition of this medium is: 
Dibasic potassium phosphate 0.2% 
Peptone 1.0% 
Agar 1.5% 
Lactose 1.0% 
Eosine 0.04% 
Methylene blue 0.01% 
By the use of this medium it is possible, with practice, to differentiate bac- 
teria of the coli type from those of the aerogenes type. While this medium does 
not positively differentiate these organisms, one experienced in its use can dif- 
ferentiate between these types in about 90% of the cases. 
